A class of letter quality printers have been developed which are commonly referred to as daisy wheel printers. Two of the better known of these types of printers are the Diablo and Qume printers.
Common to this type of printer is a circular print wheel which is constructed with a plurality of radial projecting spokes, usually about 100 spokes, each of which spokes has a raised character font on its distal end. If such print wheel is rotated next to a platen of a typewriter and a hammer impacts on the face of the spoke on the side opposite of the font, the latter will be driven toward the platen so that font will be impressed against the platen. With a ribbon and paper located between the font and the platen, printing of a character will be accomplished when the hammer impacts on the distal end of a spoke. Because the ends of the spokes are distorted out of the radial plane of the disc element as the hammer impacts, these wheels are called daisy wheels by analogy to the petals of the flower, commonly referred to as a daisy having radial extending petals.
Typically these daisy wheels are of a unitized construction having a hub to which the spokes are attached and from which they radiate. In the hub of a typical wheel is a bore in which the shaft of a drive motor can be received. Also a notch or some other indexing means is formed in the hub structure so that an indexing pin associated with the motor shaft will be received therein, ensuring the proper angular registry or correspondence between the shaft and the spokes of the print wheel.
Digital logic controls the rotation of the motor shaft and the timing for the imacts of the hammer. To enable the replacement of the print wheel in these machines, the motor and hammer assembly is usually mounted on a carriage which pivots away from the platen of the typewriter (See FIG. 1) so the print wheel can be removed axially from the end of the motor shaft since the wheel must be very close to the platen during printing so the deflection of the spokes will be minimal, when the hammer impacts thereon.
Normally the motor shaft will extend into the hub of the print wheel about 1/2-inch to properly stabilize it so it will rotate without wobble or flutter. Thus considerable space is required to replace the print wheels in these type of printers and it is necessary to pivot the carriage to withdraw the print wheel from its position adjacent to the platen to enable replacement thereof.
The current invention is an improved print wheel which can be inserted or removed vertically, i.e., normal to the axis of the motor shaft, whereby the carriage mechanisms can be greatly simplified in these types of printers since the motor and hammer assembly does not have to be pivoted to change wheels.